1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a back light assembly for maximizing a light incident efficiency by changing a structure of a light guide plate for guiding lights from a lamp to a display unit for displaying images and a liquid display device having the same.
2. Description of the Related Art
At the present time, information processing devices are rapidly developing with trends towards various architectures, functions and faster information processing speed. Information processed in these information processing devices has an electrical signal format. In order to visually confirm information processed in an information processing device, a display should be provided as an interface device. An example of such a display device is the liquid crystal display (LCD).
LCDs offer numerous advantages as display devices such as light weight, small size, high resolution, and low power consumption. They are also environmentally friendly and they offer a display of full colors compared with the traditional cathode ray tube (CRT). Such advantages allow the LCDs to replace the CRTs and to be recognized as a next generation display.
LCDs apply electric power to liquid crystal having a specific molecular configuration so as to vary the molecular arrangement of the liquid crystal. The variation in the molecular configuration of the liquid crystal causes a variation in optical properties such as birefringence, optical rotary power, dichroism and light scattering. The LCDs utilize such variations in optical properties to display an image.
In the LCD device, functions of a backlight assembly bring attention to a more important problem. The reason is that the backlight assembly affects both the mechanical and optical characteristics of the LCD device such that the size and the light efficiency of the LCD device undergo a change. This is discussed, along with a description of prior art systems, in conjunction with FIGS. 1–3 below.
FIG. 1 is an exploded perspective view schematically showing the LCD device according to the conventional art schematically. FIG. 2 is a sectional view schematically showing the constructions of a lamp unit and a light guide unit in the backlight assembly as shown in FIG. 1. FIG. 3 is a view showing a pathway of the light in the light guide plate shown in FIG. 2.
Referring first to FIG. 1, the LCD device 900 has a LCD module 700 for displaying images when image signals are applied thereto and a case (not shown) for receiving the LCD module 700. The LCD module 700 includes a display unit 710 having a LCD panel for showing the images.
The display unit 710 includes the LCD panel 712, a data-side printed circuit board (PCB) 714, a gate-side PCB 717, a data-side tape carrier package 716 and a gate-side tape carrier package 718.
The LCD panel 712 includes a thin film transistor substrate 712a, a color filter substrate 712b and liquid crystal (not shown) between the thin film transistor substrate 712a and the color filter substrate 712b. 
The thin film transistor substrate 712a is a transparent glass on which the thin film transistors are formed in a matrix form. Data lines are respectively connected with source terminals of the thin film transistors and gate lines are connected with gate terminals of the thin film transistors. Furthermore, pixel electrodes are respectively formed at drain terminals of the thin film transistors, which are made of a transparent conductive material such as Indium Tin Oxide (ITO).
The color filter substrate 712b is provided to face the thin film transistor substrate 712a. RGB pixels are formed on the color filter substrate 712b by means of a thin film process, which presents a predetermined color while the light passes through the color filter substrate 712b. Common electrodes made of the ITO are coated on the front surface of the color filter substrate 712b. 
When the thin film transistors of the thin film transistor substrate 712a are turned on, an electric field is created between the pixel electrodes of the thin film transistor substrate 712a and the common electrodes of the color filter substrate 712b. The electric field causes the liquid crystal to change the array angle, which results in the permeability of the light being changed. As a result, the desired pixels are obtained.
A driving signal and a timing signal are applied to the gate lines and data lines of the thin film transistor in order to control the array angle of the liquid crystal and the time of arraying the liquid crystal in the LCD panel 712. A source part for providing the data driving signal to the LCD panel 712 is formed on the data-side PCB 714, and a gate part for providing the gate driving signal to the gate lines is formed on the gate-side PCB 717. In other words, the PCBs 714 and 717 generate and apply the gate driving signal and the data signal for driving the LCD device as well as a plurality of timing signals for applying the gate driving signal and the data signal to the gate lines and the data lines of the LCD panel 712.
Continuing with FIG. 1, the backlight assembly 720 is provided under the display unit 710 so as to uniformly supply the light to the display unit 710. The backlight assembly 720 includes a lamp 721 for generating the light. The lamp 721 is protected by means of a lamp cover 722.
The light guide plate 724 has a size corresponding to that of the liquid crystal panel 712 of the display unit 710, which is disposed under the liquid crystal panel 712 to guide the light emitted by the lamp 721 toward the display unit 710 by changing a pathway of the light.
A plurality of optical sheets is provided on the light guide plate 724 so as to uniformly adjust the brightness of the light that transmitted from the light guide plate 724 to the LCD panel 712. In addition, a light reflecting plate 728 is provided under the light guide plate 724 to reflect the light, which is leaked from the light guide plate 724, towards the light guide plate 728 so as to improve the efficiency of the light.
The display unit 710 and the backlight assembly 720 are supported by means of a mold frame 820 used as a receptacle. The mold frame 820 is provided with a chassis 740 for preventing the display unit 710 from departing from the mold frame 820 while the data-side PCB 714 and the gate-side PCB 717 are bent towards the outside of the mold frame 820 and are fixed to the bottom surface of the mold frame 820.
Referring now to FIG. 2, the light guide plate 724 is of an edge-type having a uniform thickness, and a lamp 721 for supplying the light is provided at an end of the light guide plate 724. Typically, the light emitted from the lamp 721 of the edge-type light guide plate 724 is transmitted through a pathway as shown in FIG. 3.
As shown in FIG. 3, the light emitted from the lamp 721 is transmitted to the top and bottom surfaces 724a and 724b of the light guide plate 724 according to the incidence angle thereof. A part of the light transmitted to the top surface 724a of the light guide plate 724 is provided to the display unit 710 after passing through the top surface 724a of the light guide plate 724, while the remainder of the light is reflected at the bottom surface 724b of the light guide plate 724 and then transmitted toward the top surface 724a of the light guide plate 724.
Meanwhile, the light transmitted to the bottom surface 724b of the light guide plate 724 is reflected by means of printed patterns (not shown) that are formed on the bottom surface 724b of the light guide plate 724, and then the light passes through the top surface 724a of the light guide plate 724. Ultimately, the light is provided to the display unit 710. At this time, a part of the light transmitted to the bottom surface 724b of the light guide plate 724 passes through the bottom surface 724b and leaks out of the light guide plate 724. However, the leaked light is reflected to the display unit 710 by means of the light is reflecting plate 728 that is disposed between the light guide plate 724 and the mold frame 820 (see FIG. 1).
With relation to the light guide plate 724, the brightness of the light that is supplied to the display unit 710 increases in proportion to the thickness of the light guide plate 724. Accordingly, a method of increasing the thickness of the light guide plate 724 can be adopted to maximize the incidence efficiency of the light. When the thickness of the light guide plate 724 increases, however, there is a problem in that the LCD device becomes heavier and has an increased thickness.